In Mexico, federal authorities continue to investigate police corruption in the northern state of Chihuahua, where 13 state police officers were arrested Thursday. Federal investigators say the accused men were involved in the death of 11 people whose bodies were discovered buried in a residential section of the border city of Ciudad Juarez. Authorities believe the murders in Juarez are part of a drug war that is raging along the U.S.-Mexico border.

Violence and drug-related crime have become common features of life in Juarez, but authorities say the discovery of the clandestine graves in a middle class neighborhood could signal an intensification in gangland warfare. The arrest of the 13 police officers and their quick transport to Mexico City also shows the seriousness which federal authorities attach to the case. Federal agents continue to search for four other police officers who are presumed to have fled justice. Investigators say the police officers, including some commanders, were working for drug traffickers who are attempting to eliminate rivals in the border region.

Mexican Attorney General Rafael Macedo de la Concha says the federal government stepped into this case because of the involvement of organized crime. He says the accused police officers are being charged with burying the bodies in Juarez as well as kidnapping and murder. He says federal investigators know these crimes were ordered by a criminal organization. In Mexico, such crimes as murder fall under the jurisdiction of state police, but federal police have authority to investigate organized crime.

In this case, the chief suspect is the so-called Juarez cartel, which investigators say is the drug smuggling operation of Vicente Carrillo Fuentes, who inherited the organization from his brother, Amado Carrillo Fuentes, known as "the Lord of the Skies," after he died in 1997.

Authorities see the clandestine graves in Juarez as part of an overall wave of violence in which drug gangs are fighting with each other for part of the lucrative smuggling business. In recent months there have been dozens of killings in Nuevo Laredo, across the border from Laredo, Texas. That city had been relatively quiet until last year when drug gangs went into open warfare with each other. Three people died in a shooting there last weekend.

In recent days there have also been other major acts of violence blamed on drug traffickers, including the murder of a former state prosecutor and three other people at a restaurant in the western border city of Tijuana and the ambush of a vehicle near Mexico City that left two federal agents and an army captain dead.

Meanwhile, federal agents continue their grim work in the residential area in Juarez where the 11 bodies were found earlier this week. A man detained in connection with the case has admitted to helping in the killings and has told police that if they keep digging they will find more bodies.